Simultaneous switching noises (SSN) are typically generated due to inductive components of conductive lines (e.g., interconnection lines) included in electronic circuits when the electronic circuits operate with high frequency signals. These simultaneous switching noises are subject to Faraday's law of induction. According to Faraday's law of induction, a counter electromotive force (e.g., a voltage drop) may be generated between both ends of a conductive line (e.g., a conductive coil) when an alternating current (e.g., an instantaneous current) flows through the conductive line to change a magnetic field around the conductive line. In such a case, the counter electromotive force may increase as the amount of the instantaneous current, the variation rate of the instantaneous current, or the inductance of the conductive line increases. The counter electromotive force generated by the instantaneous current may cause a voltage fluctuation of a power line and/or a ground line of an electronic circuit including the conductive line, and the voltage fluctuation may generate noises which are referred to as the simultaneous switching noises. The counter electromotive force (Vnoise) may be expressed by the following equation.Vnoise=−L(di/dt)
where, “L” denotes an inductance value of the conductive line.
Accordingly, if a number of circuit elements are simultaneously switched on/off, instantaneous changes in current across the power line and the ground line may occur. As a result, inductive voltage drops may occur to increase the simultaneous switching noises in the electronic circuits, for example, semiconductor systems. The simultaneous switching noises may cause signal delays to degrade the reliability of the semiconductor systems.
Each of the semiconductor systems may include various internal circuits, and each of the internal circuits may be configured to include a number of MOS transistors. The MOS transistors may be used as switches to operate the internal circuits. Recently, as the semiconductor systems become more highly integrated, a number of signals and data may be simultaneously transmitted through a number of signal lines or a number of input/output (I/O) lines. If a number of signals and data are simultaneously transmitted, a number of MOS transistors may also be simultaneously switched on/off to cause a number of simultaneous switching noises.